Abs polymer blends for high-shear processing

ABSTRACT

When a small amount of a relatively low molecular weight terpolymer of styrene, acrylonitrile and a saturated higher fatty alcohol ester of acrylic acid or methacrylic acid is incorporated into a conventional high impact grade ABS thermoplastic resin, the resin blend may be more readily subjected to high-shear forming processes to produce high-quality parts. The presence of the terpolymer in an ABS resin melt improves melt flow properties in extrusion or injection molding operations by markedly reducing melt viscosity and increasing melt stability.

United States Patent Inventor Hldeo Kubota Rosevllle, Mich.

Applv No. 54,629

Filed July 13, 1970 Patented Nov. 30, I971 Assignee General Motors Corporation Detroit, Mich.

ABS POLYMER BLENDS FOR HIGH-SHEAR PROCESSING [5 6] References Cited FOREIGN PATENTS 1,024,778 4/1966 Great Britain 260/893 Primary ExaminerMurray Tillman Assistant Examiner-C. Seccuro Attorneys-William S. Pettigrew and George A. Grove ABSTRACT: When a small amount of a relatively low molecular weight terpolymer of styrene, acrylonitrile and a saturated higher fatty alcohol ester of acrylic acid or methacrylic acid is incorporated into a conventional high impact grade ABS thermoplastic resin, the resin blend may be more readily subjected to high-shear forming processes to produce high-quality parts. The presence of the terpolymer in an ABS resin melt improves melt flow properties in extrusion or injection molding operations by markedly reducing melt viscosity and increasing melt stability.

ABS POLYMER BLENDS FOR HIGH-SHEAR PROCESSING This invention relates to high-shear processing of acrylonitrile-butadiene-styrene (ABS) resins, such as injection molding or extrusion operations. More particularly, this .nvention relates to the use of blends of a major portion of a conventional ABS resin with a minor portion of a terpolymer of styrene, acrylonitrile and certain acrylate-fatty alcohol esters, which terpolymer markedly reduces the melt viscosity of the blend, particularly at high shear rates.

The utility of ABS engineering plastics is well recognized. These hard, tough, durable synthetic resins find many applications and they may be formed by any of a number of processes. ABS resins are two-phase materials consisting of rubbery polybutadiene particles in a hard styrene-acrylonitrile plastic matrix. Generally, the ABS resin contains 20 to 30 percent polybutadiene and the balance styrene-acrylonitrile copolymer. Typically, acrylonitrile makes up 22 to 26 percent or more by weight of the copolymer. The resins may be prepared by simply mixing polybutadiene with styreneacrylonitrile copolymer, or some styrene-acrylonitrile may be chemically grafied to the polybutadiene. I

ABS resins have weight average molecular weights from around 70,000 to 250,000. High impact strength ABS resins typically have relatively high molecular weights and a higher density of network structures between the polybutadiene rubber molecules and the styrene-acrylonitrile copolymer plastic portion. ABS resin articles, including those of high-impact resin, are often formed or desired to be formed by extrusion or by injection molding. In these processes the resin is initially melted by heating to a temperature of about 450 to 500 F. and then extruded through a die or injected into a mold. Molten ABS resins, and particularly high impact grade ABS resins, have relatively high melt viscosities over a wide range of shear rates. This high viscosity makes it very difficult to injection mold high impact grade ABS resins below their decomposition temperature. Moreover, there are limitations on the shear rate at which ABS resins can be extruded or injection molded. 1f the molten resin is sheared at too high a rate, melt fracture occurs. Melt fracture is an instability in resin melt flow through a die starting at the entry to the die. It leads to unsightly surface irregularities on the molded article. Problems with painting, electroplating and long term service under load are encountered. Thus the high ABS melt viscosity limits the ease and rate of production of ABS resin articles by high-shear processes, such as injection molding or extrusion. This limitation is particularly pronounced in those high molecular weight ABS resins which have desirable high impact strength.

Accordingly, it is an object of the present invention to provide an ABS resin-terpolymer additive blend particularly suitable for use in high shear forming processes and injection molding.

It is another object of the present invention to provide a polymeric plasticizing material for mixing with ABS resins particularly for use in high shear fonning processes. The polymeric additive is to have the efiect of reducing the melt viscosity of ABS resins and increasing the melt stability of the resin, particularly at high shear rates.

In accordance with a preferred embodiment of my invention, these and other objects are accomplished by providing a terpolymer of acrylonitrile, styrene and a saturated higher fatty alcohol ester of acrylic acid or methacrylic acid. Examples of suitable terpolymers are styrene-acrylonitrile-stearyl methacrylate, styrene-acrylonitrile-stearyl acrylate and styrene-acrylonitrile-lauryl methacrylate. The number average molecular weight of these terpolymers should be at least about 5,000. The terpolymer is blended with a conventional ABS resin in the amount of about to percent by weight of the ABS resin-terpolymer mixture. The ABS resinterpolymer additive blend is then mixed and heated to a suitable molding or extrusion temperature, such as about 425 to 500 F. The resin melt is readily extruded or injected into a mold cavity under high pressure at a high shear rate. The terpolymer additive is compatible with ABS resins and markedly reduces the melt viscosity of the blend, permitting high shear rates and maintaining suitable melt stability. These ABS resinterpolymer blends may also contain a small amount of conventional lubricants which typically enhance the flow properties of ABS resin melts at low shear rates but have little efiect on melt viscosity at high shear rates.

These and other objects and advantages of my invention will be more fully understood in view of a detailed description thereof which follows.

Terpolymer additives which are useful in accordance with my invention are those formed by the interpolymerization of styrene, acrylonitrile and esters of acrylic acid or methacrylic acid and certain saturated high fatty alcohols. In accordance with this invention, higher fatty alcohols are those straightchain alcohols having 12 to 18 carbon atoms in the molecule. Particularly preferred are the lauryl and stearyl alcohol esters of acrylic and methacrylic acid.

The terpolymer additives can be prepared by solution polymerization in carbon tetrachloride which acts both as solvent and chain transfer agent. The free radical polymerization can be initiated, for example, by azo-iso-butyronitrile. The polymerization is carried out under nitrogen atmosphere and the reaction temperature is easily kept at the boiling temperature of carbon tetrachloride (76 C.). Preferably, styrene and acrylonitrile are charged to the solution for polymerization in such proportions that acrylonitrile constitutes about 22 percent to 28 percent of the sum of these two monomers. The fatty alcohol ester of acrylic acid or methacrylic acid is added in an amount equivalent to about 1% to 10 mole percent of the total monomer mixture for polymerization. The specific proportions of the mer units of the resulting terpolymer are not specifically known, but the terpolymer should have a number average molecular weight, in accordance with this invention, of at least about 5,000. Solution polymerization can be used to produce these terpolymers in the molecular weight range of about 5,000 to about 30,000. Other well-known polymerization techniques, such as bulk or emulsion polymerization, will produce higher molecular weight terpolymers.

A few specific examples of the preparation of suitable terpolymers and their use in ABS resins will further serve to illustrate the invention.

EXAMPLE I A solution of 1.31 moles (136 grams) of styrene, 0.74 mole (39 grams) acrylonitrile, 0.059 mole (20 grams) stearyl methacrylate and 1.20 grams azo-iso-butyronitrile were dissolved in 460 milliliters of carbon tetrachloride. The solution was refluxed for 8 hours under nitrogen. The polymeric product was precipitated from the solution by a large amount of methanol. It was washed with cold methanol and dried. The terpolymer was found to have a number average molecular weight of about 17,000. Infrared spectrographic analysis detected the presence of styrene, acrylonitrile and stearyl methacrylate moieties in the terpolymer product. This terpolymer No. l was blended in varying proportions, from 8.2 percent by weight to 28.5 percent by weight of the blend, with a pure commercial high impact grade acrylonitrile-butadienestyrene resin.

The pure commercial resin had such a high melt viscosity that it could not be injection molded even into a small part such as a heat deflection test sample. Examination of the resin revealed that it contained about 65 percent by weight free (acetone extractable) styrene-acrylonitrile copolymer (SAN) and that the number average molecular weight of the SAN by gel permeation chromatography was about 130,000. However, blends of this ABS resin and others with the terpolymers of my invention could be satisfactorily injection molded at 465 F.

In order that the properties of my terpolymer-ABS resin blends could be evaluated more quantitatively and more satisfactorily compared with conventional ABS resins, viscosity measurements at 240 C. (464 F.) with increasing shear rates were made using an lnstron Capillary Rheometer. The viscosity data obtained with above ABS resin-terpolyme. No. l blends is summarized in the table following example Ill. As is only a very modest effect in decreasing melt viscosity at a shear rate of 2,000 of higher seconds.

In sharp contrast, however, the viscosity data above and actual injection molding experience both show that addition of seen in the table and as will be discussed in more detail below, 5 my terpolymers to commercial ABS resins produces desirable my terpolymer-ABS resin blends displayed markedly lower low melt viscosities at high shear rates, particularly above melt viscosity, particularly at high Shear rates, than were ob- 2.000 seconds". Moreo er, these ABS resin-terpolymer tained with the pure commercial ABS r in o with th Same blends resisted or entirely eliminated melt fracture at these commercial ABS resin containing about 2.l percent by weight g Shea! rates p to 15,000 Seconds-'- fa mer i l rosin i b i m Preferably, the terpolymers of this invention are employed in amounts equivalent to 5 to percent by weight of the ABS EXAMPLE ll resin-terpolymer mixture. Quantities lower than 5 percent by A solution of 139 m 0| es (136 grams) styrene 074 m 01 e weight do not markedly improve melt properties at high shear (39 grams) acrylonitrile, 0.015 mole (4.9 grams) stearyl acryl 5 z i i g P g f by x gr i late and 3.0 grams azo-iso-butyronitrile in 500 milliliters in t es carbon tetrachloride was prepared. The solution was heated at Typical extrusion and ln ectlon moldlng processes with ABS reflux for 12 hours. The polymer was isolated, purified and resins are conducted at shear rates of 200 to 3,000 seconds dned as m example I. The number average molecular weight or higher. Of course, the higher the shear rate the more of the polymer was determined to be about 12,000. infrared 20 spectrographic analysis detected the presence of styrene production S be opwned lonmfle and Stea ac late monomeric units in the Commercial lubricants for ABS resins may be employed In a I met roduct ry ry combination with the terpolymers of my invention to obtain 228. 1 2 l8 5 d 81 5 benefits at low shear rates if desired. Examples of such lubri- .pans) was mlxe w] cants include rosin, stearic acid and other fatty acids, fatty parts of the commercial ABS resin on a heated two-roll mill at d ml t t h l d t t d 350 F. for 15 minutes. Viscosity measurements of this blend me 8 em a as ea s stearate, barium stearate, calcium stearate and zinc stearate.

at and at Increasing shear {ates .were determmed as m As exemplified in the above table, such lubricants in combinaexample. T results of these viscosity measurements are tion with ABS resin or with my ABS resin-terpolymer blends summanzed m the table below reduce melt viscosities at low shear rates but have little or no effect at shear rates.

As indicated above, it is preferred that my styrene- A solution of mole g Styrene, mole acrylonitrile-acrylic acid-fatty alcohol ester terpolymers have B acrylonlu'llei 30 grams lauryl methaclylale a number average molecular weight of at least about 5,000. In mcfclal grade-n0! P and grams am-isobutyroniu'ile general, the upper limit on the molecular weight will be that in 500 milliliters carbon tetrachloride was prepared. The solub i bl b polymerization h i i l i tion was heated at reflux under nitrogen for 12 hours. The polymerization h upper li i i bo 30,000, o h resu t g polymer a so ated, pu ifie and dried as in exampolymerization techniques produce much higher molecular pie I. It was determined to have a number average molecular weight terpolymers. This upper limit is not critical to the sucweight of about 8,000. Infrared analysis of the isolated 40 cessful practice of my invention. However, it has been ob polymer indicated the presence of styrene-acrylonitrile and served that it is desirable to blend relatively low molecular lauryl methacrylate monomeric units in the polymer. This terweight terpolymer additives with high molecular weight ABS polymer No. 3 (l8.5 parts) was blended with 81.5 parts of the resins and vice versa. In other words, when extremely high commercial ABS resin ona heated two-roll mill at 350 F. for molecular weight ABS resins (M, of free SAN portion 15 minutes and viscosity measurements at 240 C. at increas- 100,000 to 200,000) are to be formed by a high shear rate ing shear rates made as described in example l. The results of process, maximum benefits of my invention will be obtained the viscosity measurements are summarized in the table imusing a relatively low molecular weight terpolymer (M, mediately below. 5,000 to 30,000). If lower molecular weight ABS resins (M, of

VISCOSITY (POISE) AT 240 C.

'Ierpolymer #1 plus Shearrate ABS ABS plus lubri- Terpolymer Terpolymer (second (pure) lubricant l 8.2% 18. 5% 28. 5% cant #2, 18. #3, 18. 5%

4x10 s.7 10= 7.5 10= 7. 7x10 6.0)(10 4.4x10 3.s 10= 3.5x10 5.0x10= 1x10 3.9x10= 315x10 3.4x10 2.8X10 2.1x10 2.0x10 2.15X10 2.6X103 2x10 2.1 10 205x10 1.9x10= 1.6 10 1.3x10 1 1.29x10 1 36X103 1.55x10= 4x10 M.F. M.F. 1.05 10= 9.0x10= 7.3 10 7. 2x10 212x10 9.0x10 3 5x10 M.F M.F. M.F. 7.4x10 6.3 10 6.1)(10 6 95x10: 14x10: 8X10 M.F M.F. M.F. 5.0X10 4.3)(10 4.2)(10 4.s 10 5.0X102 1.5X-10 M.F M.F. M.F. M.F. 2.9 10 2. 8x10 2. 9x10 2.9 10

1 Commercial lubricant (approximately 2.1% by weight).

Nors.-M.F.=Melt Fracture observed.

The viscosity data in the above table reflects the experience free SAN portion 50,000 to 100,000) are to be formed they one observes in high-shear processes with the commercial will be advantageously blended with higher molecular weight high impact grade ABS resins and the ABS resin-terpolymer terpolymers (M,, 100,000 to 200,000). The explanation for compositions of my invention. It will be noted that with each this observation may be that it is apparently the molecular material tested, the melt viscosity decreased with increasing weight of the SAN component of an ABS resin which most sigshear rate. However, both the pure ABS resin and the ABS nificantly affects the resin's melt viscosity at high shear rates. resin containing the rosin lubricant yielded viscosity data only When a terpolymer of this invention is selected which has a at shear rates from 400 seconds to 2,000 seconds. At molecular weight different than the molecular weight spread higher shear rates melt fracture occurred, which in a shear of the SAN component, the molecular weight distribution of fonning process would prohibit satisfactory injection molding. the blend is broadened. The average molecular weight of While the commercial rosin lubricant improved flow proper- SAN-like materials is broadened and the melt viscosity of the ties by decreasing melt viscosity at low shear rates, it did blend at high shear rates is significantly reduced.

nothing to prevent rnelt fracture at high shear rates and had While my invention has been described in tenns of a few specific embodiments thereof, it will be appreciated that other fonns could readily be adapted by one skilled in the art. Accordingly, the scope of my invention is to be considered limited only by the following claims.

What is claimed is: 1. In the method of fonning acrylonitrile-butadiene-styrene (ABS) resins into useful articles by melting a said resin, subjecting said resin to high-shear processing and then cooling and solidifying said resin in a predetermined desired shape, the improvement comprising incorporating a terpolymer additive into said ABS resin prior to said processing in an amount of 5 to 20 percent by weight of the ABS resin-terpolymer mixture, said terpolymer being styrene-acrylonitrile-X, wherein X is a material selected from the group consisting of acrylic acid esters and methacrylic acid esters of saturated straightchain fatty alcohols, said fatty alcohols containing 12 to 18 carbon atoms, said terpolymers having a number average molecular weight greater than about 5,000,

the effect of the presence of said terpolymer in said ABS resin during high-shear processing being to reduce the melt viscosity at high shear rates.

2. The improved process of claim 1 wherein said terpolymer which is employed is styrene-acrylonitrile-stearyl methacrylate.

3. The improved process of claim 1 wherein the said terpolymer which is employed is styrene-acrylonitrile-stearyl acrylate.

4. The improved process of claim 1 wherein said terpolymer which is employed is styrene-acrylonitrile-lauryl methacrylate.

5. A method of forming high impact grade acrylonitrile-butadiene-styrene (ABS) resins into useful articles by the highshear processing of a melt of said ABS resin comprising preparing a molten mixture of about to parts by weight of a said ABS resin and about five to 20 parts by weight of a styrene-aerylonitrile-X terpolymer, wherein X is a material selected from the group consisting of acrylic acid esters and methacrylic acid esters of saturated straight-chain fatty alcohols, said fatty alcohols containing 12 to 18 carbon atoms, said terpolymers having a number average molecular weight of about 5,000 to 30,000, said ABS resin containing a styrene-acrylonitrile copolymer portion having a number average molecular weight of about 100,000 to 200,000,

subjecting said molten mixture to a shearing force to form it into a desired predetermined configuration and cooling said molten mixture to solidify it.

6. A method as in claim 5 wherein X is a monomer taken from the group consisting of stearyl acrylate, stearyl methacrylate, lauryl acrylate and lauryl methacrylate.

t i i 1! t (5/69) UNITED STATES PATENT OFFICE CERTIFICATE OF, CORRECTION Patent No. 3,624, 182 Dated November 30, 1971 InvenrorL's) v Hideb Kubota It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 32, "450" should be 425 "P r b Column 3, in the table entitled "Viscosity (Poise) at 240 c." the footnote l reading "Commercial lubricant (approximately 2.1% by weight). should also refer to the column entitled "28.5% plus lubricant". column 4, line 2, after 2,000" change "of" to or Signed and sealed this 16th day of May 1972.

(SEAL) Arte :3 i;

ROBERT GOTTSCHALK fattest mg Officer Commissioner of Patents 

2. The improved process of claim 1 wherein said terpolymer which is employed is styrene-acrylonitrile-stearyl methacrylate.
 3. The improved process of claim 1 wherein the said terpolymer which is employed is styrene-acrylonitrile-stearyl acrylate.
 4. The improved process of claim 1 wherein said terpolymer which is employed is styrene-acrylonitrile-lauryl methacrylate.
 5. A method of forming high impact grade acrylonitrile-butadiene-styrene (ABS) resins into useful articles by the high-shear processing of a melt of said ABS resin comprising preparing a molten mixture of about 80 to 95 parts by weight of a said ABS resin and about five to 20 parts by weight of a styrene-acrylonitrile-X terpolymer, wherein X is a material selected from the group consisting of acrylic acid esters and methacrylic acid esters of saturated straight-chain fatty alcohols, said fatty alcohols containing 12 to 18 carbon atoms, said terpolymers having a number average molecular weight of about 5,000 to 30,000, said ABS resin containing a styrene-acrylonitrile copolymer portion having a number average molecular weight of about 100,000 to 200,000, subjecting said molten mixture to a shearing force to form it into a desired predetermined configuration and cooling said molten mixture to solidify it.
 6. A method as in claim 5 wherein X is a monomer taken from the group consisting of stearyl acrylate, stearyl methacrylate, lauryl acrylate and lauryl methacrylate. 